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SPFA+0/1分數規劃。

CODE:

?

#include?<iostream>
#include?<cstdlib>
#include?<cstdio>
#include?<cstring>
#include?<queue>
using?namespace?std;

#define?MAXN?1010
#define?INF?0X3F3F3F3F
#define?eps?1e-7

struct?Edge
{
????int?v,?next;
????double?w;
}edge[MAXN*5];

double?d[MAXN],?num[MAXN];
int?first[MAXN];

int?n,?m,?cnt;

void?init()
{
????cnt?=?0;
????memset(first,?-1,?sizeof(first));
}

void?read_graph(int?u,?int?v,?double?w)
{
????edge[cnt].v?=?v,?edge[cnt].w?=?w;
????edge[cnt].next?=?first[u],?first[u]?=?cnt++;
}

int?spfa(int?src,?double?mid)
{
????queue<int>?q;
????bool?inq[MAXN]?=?{0};
????int?ct[MAXN]?=?{0};
????for(int?i?=?1;?i?<=?n;?i++)?d[i]?=?(i?==?src)?0:INF;
????q.push(src);
????while(!q.empty())
????{
????????int?x?=?q.front();?q.pop();
????????inq[x]?=?0,?ct[x]++;
????????if(ct[x]?>=?n)?return?0;?//存在負環?
????????for(int?e?=?first[x];?e?!=?-1;?e?=?edge[e].next)
????????{
????????????int?v?=?edge[e].v;
????????????double?w?=?-num[v]?+?mid*edge[e].w;
????????????if(d[v]?>?d[x]?+?w)
????????????{
????????????????d[v]?=?d[x]?+?w;
????????????????if(!inq[v])
????????????????{
????????????????????inq[v]?=?1;
????????????????????q.push(v);
????????????????}
????????????}
????????}
????}
????return?1;
}

double?BSearch()
{
????double?x?=?0,?y?=?100.0,?ans;
????while((y-x)?>?eps)
????{
????????double?mid?=?x+(y-x)/2;
????????if(spfa(1,?mid))
????????{
????????????ans?=?mid;
????????????y?=?mid;
????????}
????????else?x?=?mid;
????}
????return?ans;
}

int?main()
{
????scanf("%d%d",?&n,?&m);
????init();
????for(int?i?=?1;?i?<=?n;?i++)
????{
????????scanf("%lf",?&num[i]);
????}
????while(m--)
????{
????????int?u,?v;
????????double?w;
????????scanf("%d%d%lf",?&u,?&v,?&w);
????????read_graph(u,?v,?w);
????}
????double?ans?=?BSearch();
????printf("%.2lf\n",?ans);
????return?0;
}

?

轉載于:https://www.cnblogs.com/g0feng/archive/2012/10/24/2737665.html

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